On Wed, 13 Apr 2016, Rick Bensene wrote:
Bill Degnan wrote:
I replaced my filters a little while ago, I was concerned about original
filters'
deterioration, perhaps these will have decomposed over time even if not in
use. So I found a newly-produced filter, documented here:
http://vintagecomputer.net/browse_thread_record.cfm?id=588&tid=1
But basically 3M Filtrete #0412560 carbon pre-filter cut to match the original,
from a tracing.
The filter Bill replaced is the external dust filter. While good to replace,
this isn't the internal HEPA filter that Michael wrote about replacing on his
RK05 drives, and that he found available on eBay.
The HEPA filter is inside the drive. It is a filter designed to capture very
tiny particles yet still be a minimal restriction to airflow. To get to the
HEPA filter, you have to take the bottom cover off of the drive. The filter
is quite large, and as mentioned, there are two different types depending on
the age of the drive. If they haven't been replaced in a long time, they
should be replaced, as they eventually do clog up with particulates. When this
happens, it can restrict the airflow to the disk platter area, which can lead
to dust particles ending up on the platter, and that can result in head
crashes, which are most unpleasant. Sadly, the manufacturer of the HEPA
filter stopped making them a long time ago, and they can be hard to find. I do
believe some manufacturer was making reproductions of them for a time, but I
believe that they are no longer doing so. So, finding the filters today can be
tricky.
-Rick
I haven't worked on such myself, but please be careful and wear a pair of
heavy gloves when servicing the HEPA filters in these old pack drives. I'm
reminded of a quote from Ralph Klimek's Burroughs page at Monash:
"They used HEPA absolute filters were a biohazard because they could trap
bacteria and fungal spores. The manuals warned about avoiding injury, with
good reason. Once a used filter I was removing slipped and I grabbed it. I
cut my hand on the dirty side of the filter element. The cut became
infected and did not heal for nearly half a year! A filter that sat idle
for a a couple of weeks would smell like a mushroom farm as the trapped
fungal spores would spawn and begin eating the trapped dust."
http://vm-118-138-243-85.erc.monash.edu.au/fixing-the-burroughs.html
Best,
Sean
